Step 1: Refraction of light
When light travels from one medium to another (in this case, from air to water), it changes its speed and direction. This phenomenon is known as refraction.
Step 2: Refraction in water
The refractive index of water is greater than that of air, causing light to bend as it passes from the air into the water. As a result, objects submerged in water appear larger or closer than they really are.
Step 3: Applying to the lemon
When you look at the lemon through the water, the light rays from the lemon bend at the surface of the water, making the lemon appear larger than its actual size. This is a classic example of refraction.
Step 4: Final Answer
The light phenomenon responsible for the lemon appearing larger than its real size is refraction.
\[
\boxed{\text{Refraction}}
\]
Two light beams fall on a transparent material block at point 1 and 2 with angle \( \theta_1 \) and \( \theta_2 \), respectively, as shown in the figure. After refraction, the beams intersect at point 3 which is exactly on the interface at the other end of the block. Given: the distance between 1 and 2, \( d = 4/3 \) cm and \( \theta_1 = \theta_2 = \cos^{-1} \frac{n_2}{2n_1} \), where \( n_2 \) is the refractive index of the block and \( n_1 \) is the refractive index of the outside medium, then the thickness of the block is cm. 
$PQ$ is a chord of length $4\ \text{cm}$ of a circle of radius $2.5\ \text{cm}$. The tangents at $P$ and $Q$ intersect at a point $T$. Find the length of $TP$.
Find the unknown frequency if 24 is the median of the following frequency distribution:
\[\begin{array}{|c|c|c|c|c|c|} \hline \text{Class-interval} & 0-10 & 10-20 & 20-30 & 30-40 & 40-50 \\ \hline \text{Frequency} & 5 & 25 & 25 & \text{$p$} & 7 \\ \hline \end{array}\]